The extreme cold of the “Uri” arctic outbreak centered on Feb. 12-18, 2021, yielded 272 U.S. gas population weight HDD which was about 80 HDD colder than the 30-year normal and 84 HDD colder than the 10-year normal. The preliminary estimate of U.S. gas population weight HDD is in the 234-244 range for the Jan. 11-17, 2024, cold outbreak.

The 12Z GFS piles snow via 4 storms (three are pictured) across the Northeast, Midwest, and South-central U.S. The snow in the East should encourage colder weather. Consequently, the warmer East U.S. midday 12Z GFS may be too warm.

A historic warm December 2023 featuring monthly temperature departures from normal of +8F to +14F across the North-central U.S. and >4F for almost the entire northern half of the U.S. are about to fade. North Atlantic oscillation (NAO) is getting ready to shift from values >+2.0 in Mid-December to an average of about -1.5 for January 5-17, 2024. Consequently, a blocking high pressure area over Greenland forces a strong longwave trough across Central Canada to the Southwest U.S. causing a snowy/colder January regime ahead.